1. Field of the Invention
This invention relates to a method of detecting a state of malfunction of an insulation resistance detecting circuit (a detector) for detecting a drop of the insulation resistance between a body of vehicle and a direct-current power supply, and the insulation resistance drop detector acting the method of detecting the state of malfunction of the detector.
2. Description of the Related Art
As an aforesaid insulation resistance drop detector, an earth detecting circuit for an electric vehicle described in Patent Document 1 exists. The electric car has a drive circuit system A including a battery unit B for a high voltage (200–300V) direct-current power supply, an inverter 2 as an AC-DC converter for converting direct current supplied through a plus bus line 4 as a positive direct-current supply electric wire and a minus bus line 5 as a negative direct-current supply electric wire from the battery unit B to alternating current, an AC motor being supplied alternating current through a U-phase line 6, a V-phase line 7 and a W-phase line 8 as alternating-current supply electric wires from the inverter 2, as shown in FIG. 4, 5. The earth detecting circuit is for detecting earth from the battery unit B to a body of vehicle E in the drive circuit system A. The earth detecting circuit includes an oscillating circuit 10 as an alternating signal output circuit and a detecting circuit 20 as a circuit for detecting voltage level change. A coupling capacitor 10A is connected with a connecting point P between the oscillating circuit 10 and the detecting circuit 20 and the plus bus line 4 of the battery unit B in the drive circuit system A, so that direct current element is cut off.
An oscillator 11 in the oscillating circuit 10 generates rectangular wave pulse having 50% duty ratio of constant frequency (see right and left charts in FIG. 5A). Thereafter, an impedance converter 12 outputs rectangular wave pulse with the same duty ratio. An alternating signal output of the oscillating circuit 10 exists at the connecting point P through a detecting resistor 13. The detecting resistor 13 functions as a voltage divider together with an insulating resistor 31 when earth is occurred.
The detecting circuit 20 includes a comparator 21 for comparing a voltage at the connecting point P between the detecting resistor 13 and the coupling capacitor 10A, in which the alternating signal output of the oscillating circuit 10 exists, and a reference voltage V1. The connecting point P is connected with an inverting input terminal of the comparator 21. A noninverting input terminal of the comparator 21 is connected with a reference voltage circuit for defining the reference voltage V1 by voltage dividing resistors 22, 23.
An output side of an operational amplifier structuring the impedance converter 12 and an input side of an operational amplifier structuring the comparator 21 are connected with diodes 15–18 for protecting the operational amplifiers from a reverse voltage or an over voltage when earth is occurred.
According to this circuit, in the state of normal when earth is not occurred, a resistance of the insulating resistor 31 shown in FIG. 4 is extremely larger than that of the detecting resistor 13. Therefore, rectangular wave pulse having a larger peak value than the predetermined reference voltage V1 is outputted at the connecting point P in which a value divided with the resistances of the insulating resistor 31 and the detecting resistor 13 exists (see a left chart in FIG. 5B).
Thereby, the rectangular wave pulse having the larger peak value than the predetermined reference voltage V1 is inputted to the inverting input terminal of the comparator 21 and a rectangular wave pulse with 50% duty ratio is outputted from the comparator 21 (see a left chart in FIG. 5C). Thereafter, a smoothed voltage Vr formed by a smoothing circuit 26 with a resistor 24 and a capacitor 25 becomes smaller than the reference voltage V1 (see a left chart in FIG. 5D) and is inputted to the noninverting input terminal of the comparator 27 so that an output of the comparator 27 becomes low level showing the state of normal (see a left chart in FIG. 5E).
When earth is occurred between the minus bus line and the body of vehicle E, and the resistance of the insulating resistor 31 shown in FIG. 4 is decreased, rectangular wave pulse having a smaller peak value than the predetermined reference voltage V1 is outputted at the connecting point P in which a value divided with the resistances of the insulating resistor 31 and the detecting resistor 13 exists (see a right chart in FIG. 5B) Thereby, the rectangular wave pulse having the smaller peak value than the predetermined reference voltage V1 is inputted to the inverting input terminal of the comparator 21 and an output from the comparator 21 is changed to 100% duty wave (see a right chart in FIG. 5C).
Thereby, the smoothed voltage Vr formed by the smoothing circuit 26 with the resistor 24 and the capacitor 25 becomes larger than the reference voltage V1 (see a right chart in FIG. 5D) and is inputted to the noninverting input terminal of the comparator 27 so that the output of the comparator 27 becomes high level showing the drop of the insulation resistance (see a right chart in FIG. 5E). Thus, the earth is detected by a logical level of the comparator 27 when the earth is occurred at the battery unit B.
The document 1 is Japan Patent Application Laid Open H8-70503.
Objects to be Solved
There is a drawback that the above earth detecting circuit cannot detect whether the earth detecting circuit itself is in state of malfunction or normal.
To overcome the above drawback, one object of this invention is to provide a method of detecting a state of malfunction of an insulation resistance drop detector and the insulation resistance drop detector acting the method of detecting the state of malfunction of the detector.
How to Attain the Object
In order to attain the objects, a method of detecting a state of malfunction of an insulation resistance drop detector according to this invention is specified in the detector having a detecting resistor connected in series with an insulating resistor between a body of vehicle and a direct-current power supply, a coupling capacitor disposed between the insulating resistor and the detecting resistor, a pulse signal generator supplying a pulse signal into a series circuit composed of the insulating resistor, the coupling capacitor and the detecting resistor, a filter for eliminating a signal having a specific frequency from a voltage at a connecting point between the coupling capacitor and the detecting resistor, and a sensor for sensing the drop of the insulation resistance based on an output from the filter, by changing a frequency of the pulse signal, and detecting the state of malfunction of the insulation resistance drop detector based on the output of the filter when the frequency is changed.
According to the above method, when the coupling capacitor is opened or the filter is in the state of malfunction, a time constant of the filter is decreased and a rising time of an output of the filter against a pulse signal output becomes shorter than that in the state of normal. The rising times of the output of the filter between in the states of malfunction and normal differ from each other so that, by changing a frequency of the pulse signal, the state of the detector can be detected based on the output of the filter when the frequency is changed.
The method of detecting the state of malfunction of the detector according to this invention is more specified in the aforesaid method by changing the frequency of the pulse signal to be increased when the detector is detecting.
According to the method described above, the frequency of the pulse signal is increased when the detector is detecting. By changing the frequency, the difference of the rising times of the outputs of the filter between in the states of malfunction and normal makes a difference of output levels of the filter. Thereby, the state of the insulation resistance drop detector can be detected based on the outputs level of the filter when the frequency is changed.
The method of detecting the state of malfunction of the detector according to this invention is further specified in the aforesaid method by detecting the state of normal of the insulation resistance drop detector when change of the output of the filter can be detected corresponding to changing the frequency of the pulse signal to be increased.
According to the method described above, the state of normal of the insulation resistance drop detector can be detected when change of the output of the filter corresponding to increasing frequency is detected, i.e. when the rising time of the output or the filter can be detected not to be shorter than that in the state of normal.
The method of detecting the state of malfunction of the detector according to this invention is further specified in the aforesaid method by outputting pulse signal of a first frequency while the detector is detecting, outputting pulse signal of a second frequency larger than the first frequency when the state of malfunction is detected, and detecting the state of normal of the insulation resistance drop detector when the output of the filter corresponding to pulse signal of the first frequency is a first predetermined value or more and the output of the filter corresponding to pulse signal of the second frequency is a second predetermined value, smaller than the first predetermined value, or less.
According to the method described above, the pulse signal of the first frequency is outputted while the detector is detecting, and the pulse signal of the second frequency larger than the first frequency is outputted when the state of malfunction is detected. When the output of the filter corresponding to the pulse signal of the first frequency is the first predetermined value or more and the output of the filter corresponding to pulse signal of the second frequency is the second predetermined value, smaller than the first predetermined value, or less, the state of normal of the detector is detected. Therefore, by comparing the output of the filter with the first and second predetermined values, change of the output of the filter can be easily judged.
The method of detecting the state of malfunction of the detector according to this invention is further specified in the aforesaid method by detecting the state of malfunction of the insulation resistance drop detector when the output of the filter is a third predetermined value or more and no change of the output of the filter can be detected corresponding to changing the frequency of the pulse signal to be increased.
According to the method described above, the state of malfunction of the insulation resistance drop detector is detected when the output of the filter is the third predetermined value or more and no change of the output of the filter can be detected corresponding to changing the frequency of the pulse signal to be increased. Thereby, when malfunction to shorten rising time of the filter against the output of the pulse signal by decreasing the time constant of the filter such as open of the coupling capacitor is occurred, the state of malfunction can be detected.
The method of detecting the state of malfunction of the detector according to this invention is further specified in the aforesaid method by detecting the state of malfunction of the insulation resistance drop detector when the output of the filter is a fourth predetermined value smaller than the third predetermined value or less and no change of the output of the filter can be detected corresponding to changing the frequency of the pulse signal to be increased.
According to the method described above, the state of malfunction of the insulation resistance drop detector is detected when the output of the filter is the fourth predetermined value smaller than the third predetermined value or less and no change of the output of the filter can be detected corresponding to changing the frequency of the pulse signal to be increased. Thereby, when malfunction not to rise the output of the filter corresponding to the output of the pulse signal such as short of the coupling capacitor or the filter is occurred, the state of malfunction can be detected.
An insulation resistance drop detector, the insulation resistance existing between a body of vehicle and a series-current power supply, according to this invention is specified by including a detecting resistor being connected in series with an insulating resistor between the body of vehicle and the direct-current power supply, a coupling capacitor being disposed between the insulating resistor and the detecting resistor, a pulse signal generator supplying a pulse signal into a series circuit composed of the insulating resistor, the coupling capacitor and the detecting resistor, a filter for eliminating a signal having a specific frequency from a voltage at a connecting point between the coupling capacitor and the detecting resistor, a sensor for sensing the drop of the insulation resistance based on an output from the filter, a changing device for changing a frequency of the pulse signal, and a detecting device for detecting state of malfunction of the insulation resistance drop detector based on the output of the filter when the frequency is changed.
According to the detector described above, when the coupling capacitor is opened or the filter is in the state of malfunction, a time constant of the filter is decreased so that a rising time of the filter against the output of the pulse signal becomes shorter than that in the state of normal. The rising times of the output of the filter between in the states of malfunction and normal differ from each other so that, by changing a frequency of the pulse signal, the state of the detector can be detected based on the output of the filter when the frequency is changed.
The above and other objects and features of this invention will become more apparent from the following description taken in conjunction with the accompanying drawings.